#lang racket
(define g '((1 2 3)
           (2 3)
           (3 4 5)
           (4)
           (5 2 4 6)
           (6 2)))

(define (keys graph)
  (map car graph))
(define vertices keys)

(define (children g x)
  (if (> x (length g)) "Error"
      (cdr (list-ref g (- x 1)))))

(define (search p l)
  (and (not (null? l))
       (or (car l) (search p (cdr l)))))
(define (search-child v f g)
  (search f (children g v)))
(define (every? p? l)
  (if (null? l) #t
      (and (p? (car l))
           (every? p? (cdr l)))))
(define (symetric g)
  (all? (lambda (u)
          (all? (lambda (v)
                  (edge? v u))
                (children g u)))
          (vertices g)))